JPH09270663A - Surface acoustic wave device - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide an elastic surface device that achieves good filter characteristics and is downsized. SOLUTION: A parallel resonator 9 and a series resonator 8 and a signal line 10 connected to both resonators 8 and 9 are arranged on a piezoelectric substrate 7, and comb electrodes of both resonators 8 and 9 are respectively arranged. So that the crossing widths of overlap in the propagation direction of the leaky surface wave,
A surface acoustic wave device 6 in which both resonators 8 and 9 are arranged, and the distance between both resonators 8 and 9 is 10 times or more the wavelength of the leaky surface wave.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device including a surface acoustic wave resonator mounted on a small mobile radio device such as a car phone and a mobile phone.

[0002]

2. Description of the Related Art At present, an elastic surface device is often used for TV, VTR, mobile communication, etc. As the elastic surface device, a comb-shaped electrode is formed on a piezoelectric substrate, and the comb-shaped electrode is used to generate an electric signal. A ladder-type circuit device for converting a surface acoustic wave into a surface acoustic wave has been proposed (JP-A-6-13837).
No.).

The elastic surface device 1 is shown in FIG.
Reference numeral 2 is a piezoelectric substrate, and 3 and 4 are a series resonator and a parallel resonator, respectively, which are arranged on the piezoelectric substrate 2. Both the resonators 3 and 4 are comb-shaped electrodes, and a pair of reflectors sandwiching the comb-shaped electrodes. Made of electrodes and. A signal line 5 is connected to each of the resonators 3 and 4.

Further, according to this surface acoustic device 1, the cross widths of the comb-shaped electrodes of both the series resonator 3 and the parallel resonator 4 do not overlap in the propagation direction of the surface acoustic wave (leakage surface wave). , Both resonators 3 and 4 are arranged, and
The out-of-band attenuation amount due to the interference of the surface acoustic waves of the two resonators 3 and 4 is prevented from deteriorating.

[0005]

However, in the elastic surface device 1 having the above structure, a plurality of series resonators 3 are provided.
Are arranged and the parallel resonators 4 are arranged between the individual series resonators 3, the area occupied by the signal lines 5 is widened, and the signal lines 5 are laid out, so that the piezoelectric substrate 2 becomes large. There was a problem. Further, when the resonators are close to each other as described above, there is a problem that the interaction between the resonators is large and the ripple (maximum insertion loss-minimum insertion loss) becomes large in the pass band.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an elastic surface device which solves the above problems, obtains good filter characteristics, and has a small piezoelectric substrate to achieve miniaturization.

[0007]

According to the surface acoustic wave device of the present invention, at least a parallel resonator and a series resonator formed of comb-shaped electrodes, and a signal line connected to both resonators are arranged on a piezoelectric substrate. In a surface acoustic wave device, both resonators are arranged so that the crossing width of each comb-shaped electrode of both resonators overlaps in the propagation direction of a leaky surface wave (leaky wave), and the distance between both resonators is leaked. The length is 10 times or more the wavelength of the surface wave. Here, between the two resonators, there is a signal line non-formation portion where no signal line or electrode is provided. Each resonator may be composed of, for example, a comb-shaped electrode and a pair of reflector electrodes sandwiching the comb-shaped electrode.

Further, the piezoelectric substrate is made of single crystal lithium tantalate (particularly, 36 ° rotation Y cut-X propagation) or lithium niobate (particularly 41 ° rotation Y cut-X propagation). .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The elastic surface device 6 according to an embodiment of the present invention will be described below with reference to the resonator layout diagram of FIG. In the figure, 7 is, for example, 36 ° rotation Y-cut-X propagation lithium tantalate (LiTaO ₃ ) or 41 ° rotation Y-cut-X propagation lithium niobate (Li.
A piezoelectric substrate made of a single crystal such as NbO ₃ ). On the piezoelectric substrate 7, a surface acoustic wave element composed of a comb-shaped electrode and a pair of reflector electrodes sandwiching the comb-shaped electrode with a metal film such as aluminum (Al) is laid in a so-called ladder type by a lift-off method or the like. .

And regarding the number of steps of this ladder type,
A 2.5-stage connection is formed in which three series resonators 8 in which comb electrodes are connected in series are provided and two parallel resonators 9 in which comb electrodes are connected in parallel are provided. A signal line 10 is connected to each of the resonators 8 and 9. It should be noted that each resonator does not necessarily have to have a reflector.

Regarding the arrangement relationship between the two resonators 8 and 9, the crossing widths of the comb-shaped electrodes of the two resonators 8 and 9 are overlapped in the propagation direction of the leaky surface wave. Here, the meaning that the crossing widths overlap in the propagation direction of the leaky surface wave will be described. When the crossing widths do not overlap in the propagation direction of the leaky surface wave, as shown in FIG.
When the cross width W1 of the comb-shaped electrodes of the series resonator 18 is separated from the cross width W2 of the comb-shaped electrodes of the parallel resonator 19 in the direction orthogonal to the propagation direction of the leaky surface wave, that is, in the propagation direction of the leaky surface wave. It is assumed that the distance X in the orthogonal direction is positive. On the other hand, when the cross widths overlap in the propagation direction of the leaky surface wave, the cross width W1 of the comb electrodes of the series resonator 18 is the cross width of the comb electrodes of the parallel resonator 19, as shown in FIG. It is assumed that the width W2 and the leaky surface wave are close to each other in the direction orthogonal to the propagation direction (the distance X in FIG. 2A is negative).

Further, between the series resonator 8 and the parallel resonator 9 (the length S in FIG. 2B), the wavelength should be 10 times (10λ) or more of the wavelength (λ) of the surface acoustic wave. The signal line non-formation portion 11 having no signal line or electrode is provided.
Here, the reason why the signal line non-formation portion 11 having a length of 10λ or more is provided is that as shown in FIG. 3, the distance between the resonators in FIG. The minimum insertion loss) is 2.5 dB or less when the distance between the resonators is 10λ or more, and the minimum insertion loss (about 1 dB) in the pass band determined by the design and manufacturing process of the surface acoustic wave filter.
And the maximum insertion loss, which is the sum of the ripples in the pass band, is 3.5 dB, which is the characteristic required for the surface acoustic wave filter.
This is because the following is satisfied.

Thus, according to the elastic surface device 6 having the above-described structure, the crossing widths of the comb-shaped electrodes of the two resonators 8 and 9 are made to overlap in the propagation direction of the leaky surface wave. , 9 approach, which causes the piezoelectric substrate 7
Becomes smaller, the surface acoustic wave device 6 can be downsized, and the surface acoustic wave device can be easily designed.

Moreover, since the signal line non-formation portion 11 having a distance of 10λ or more is provided between the two resonators 8 and 9, the leaky elastic waves of the two resonators 8 and 9 do not interfere with each other. As a result, good filter characteristics can be obtained.

[0015]

EXAMPLES Next, specific examples will be described. For the elastic surface device 6, the period of the series resonator 8 is 4.4.
μm, the period of the parallel resonator 9 was 4.6 μm, the interval S between the signal line non-formation portions 11 was 20λ, the number of reflector electrodes was 50, and the thickness of the Al electrode film was 5000 Å.

This Al electrode was formed into a film as follows. First, 36 ° rotated Y-cut-X propagation single crystal LiT
A substrate made of aO ₃ and having a thickness of about 0.5 to 1 mm is prepared, and the surface of this substrate is mirror-polished to form a piezoelectric substrate 7.
As shown in FIG. 4A, a novolac resin photoresist 12 is applied on the piezoelectric substrate 7 by a spin coating method to a predetermined thickness (about 1.5 μm), and then as shown in FIG. 4A, a resist pattern 13 is formed by photolithography, and then an Al thin film 14 is formed on the resist pattern 13 by electron beam evaporation, as shown in FIG. 4C. As described above, the required Al electrode pattern 15 was formed by a so-called lift-off method in which an unnecessary portion was peeled off with a resist solvent.

Thus, while the size (element area) of the piezoelectric substrate 2 of the conventional elastic surface device 1 is 1.7 × 2.5 mm, the size (piezoelectric substrate 7 of the elastic surface device 6 of the present invention is ( The element area) was 1.7 × 1.3 mm, and the size could be reduced to about 1/2.

Next, when the frequency characteristics of the elastic surface device 6 of the present invention and the conventional elastic surface device 1 as filter elements were measured, the results shown in FIG. The results shown in 6 were obtained. In both figures, the horizontal axis represents the span of frequency 660 to 1100 μHz, and the vertical axis represents the insertion loss.

As is apparent from these figures, the surface acoustic wave device having the conventional structure undergoes characteristic changes such as ripples in the pass band. On the other hand, in the present invention, good characteristics with a small insertion loss in the pass band and a small ripple were obtained.

For these measurements, the surface acoustic wave device is first mounted in an SMD (Surface Mounted Device) package, the package is fixed with a measuring jig, and then a network analyzer (HP8753C) is used with a coaxial cable. ) Was done by connecting to. Then, the network analyzer measured S21 (transmission characteristic), which is one of the filter characteristics.

The present invention is not limited to the above-mentioned embodiment, and various modifications and improvements may be made without departing from the scope of the present invention. For example, in this embodiment, 36 ° Y-XLiTaO ₃ is used as the piezoelectric substrate 7, but 41 ° rotation Y-cut having piezoelectricity is also used.
Good filter characteristics were obtained even when an X-propagating lithium niobate (LiNbO ₃ ) substrate was used, and the piezoelectric substrate could be made smaller and smaller.

In addition to the surface acoustic wave filter, the present invention can be applied to various surface acoustic wave devices such as a surface acoustic wave resonator, a surface acoustic wave delay line, a surface acoustic wave convolver, and a surface acoustic wave duplexer. is there.

[0023]

As described above, according to the surface acoustic wave device of the present invention, the respective crossing widths of the comb-shaped electrodes of the parallel resonator and the series resonator are made to overlap in the propagation direction of the leaky surface wave, so that the resonance is achieved. Since the resonators are brought close to each other and the distance between the two resonators is set to 10λ or more, not only the device can be downsized, but also the leaky surface waves of the both resonators do not interfere with each other. An excellent elastic surface device having very good filter properties can be provided.

Particularly, if a 36 ° Y-X LiTaO ₃ substrate or a 41 ° Y-X LiNbO ₃ substrate is adopted as the piezoelectric substrate of the surface acoustic wave device, the surface acoustic waves of these piezoelectric substrates are in modes other than leaky surface waves. As compared with the other substrate, the surface acoustic wave is greatly attenuated between the two resonators, and a very good surface acoustic wave device can be provided.

Further, by increasing the ratio of the width of the signal line between the resonators and the width of the portion where the electrode is not formed to the width between the resonators, it becomes possible to reduce the width between the resonators in the case of the same characteristics. The chip area of the surface acoustic wave device can be reduced.

[Brief description of drawings]

FIG. 1 is a resonator layout diagram schematically showing an elastic surface device of the present invention.

FIG. 2 is a resonator arrangement diagram for explaining a mode between resonators.

FIG. 3A and FIG. 3B are diagrams for explaining the relationship between the inter-resonator distance and the ripple.

4 (a) to 4 (d) are cross-sectional views illustrating a manufacturing process of the elastic surface device of the present invention.

FIG. 5 is a diagram showing frequency characteristics of the elastic surface device of the present invention.

FIG. 6 is a diagram showing frequency characteristics of a conventional elastic surface device.

FIG. 7 is a resonator layout diagram schematically showing a conventional elastic surface device.

[Explanation of symbols]

 6 ... Elastic surface device 7 ... Piezoelectric substrate 8 ... Series resonator 9 ... Parallel resonator 10 ... Signal line 11 ... Non-formation part of signal line etc.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Miki Ito, 3-5 Hikaridai, Seika-cho, Soraku-gun, Kyoto Pref., Central Research Laboratory, Kyocera Corporation (72) Inami, Emi Kakai, 3 Kitsudai, Seika-cho, Soraku-gun, Kyoto Prefecture Kyocera Co., Ltd. Central Research Laboratory (72) Inventor Masayuki Funami, 3-5 Hikaridai, Seika-cho, Soraku-gun, Kyoto Prefecture Kyocera Corporation Central Research Laboratory

Claims (2)

[Claims] 1. A surface acoustic wave device comprising a piezoelectric substrate on which parallel resonators and series resonators each composed of a comb-shaped electrode and signal lines connected to the resonators are arranged. A surface acoustic wave device characterized in that a crossing width of each comb-shaped electrode of a series resonator is overlapped in a propagation direction of a leaky surface wave, and a distance between the two resonators is 10 times or more a wavelength of the leaky surface wave. . 2. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of single crystal lithium tantalate or lithium niobate.